Osteoporosis, the progressive loss of bone tissue, affects more than 30 million Americans. Normal bone is composed of a framework made of a particular protein, collagen, and calcium salts. Osteoporosis depletes both the collagen and the calcium salts from the bone. The bone then becomes weaker and more prone to breaks (fractures), either by cracking or by collapsing (compression).
Patients with osteoporosis generally have no symptoms until bone fractures begin. Fractures of the vertebrae of the spine are usually a result of minor compression forces on bone. This leads to collapse of the vertebrae. A fracture that collapses a vertebra in this way is referred to as a vertebral compression fracture.
Spinal vertebral fractures can occur without pain. However, they often cause a severe “band-like” pain that radiates from the spine around both sides of the body. Spinal fractures cause a loss of height of the spine resulting in the person becoming shorter. A change in curvature of the spine can also occur giving the individual a hunched-back appearance (the so-called dowager's hump). This can contribute to chronic backaches.
In the past, the treatment of vertebral compression fractures has been limited to taking pain medicine, resting, avoiding injury, and bracing. More recently surgical therapies have become available for the treatment of these fractures.
Vertebroplasty is a minimally invasive procedure to treat vertebral compression fractures that is typically performed by a radiologist or orthopedic surgeon. Vertebroplasty involves injecting a cement-like material into the collapsed vertebra in order to stabilize and strengthen the crushed bone. The cement is typically inserted with a needle, catheter and/or syringe through anesthetized skin into the body of the vertebra under the guidance of specialized x-ray equipment. Once inserted, the material soon hardens, forming a cast-like structure with the locally broken bone. The advantages of vertebroplasty, aside from prompt pain relief, include better mobility.
The physio-chemical properties and fill patterns of the cement commonly employed in vertebroplasty, polymethylmethacrylate (PMMA), have been widely thought to introduce secondary bone damage and cause failure of other vertebrae—either adjacent to the “cemented” vertebra or remote vertebrae (i.e., vertebrae at least two positions removed from the “cemented” vertebra). For example, referring to FIGS. 1 and 1a, traditional PMMA bone cement materials tend to have a localized or compact distribution within the vertebra. Such compact distribution has been shown to cause stress concentrations in the bone tissue directly above and below the PMMA, which may lead to fractures of the adjacent and remote vertebrae. The stress concentrations in the bone tissue directly above and below the PMMA may also cause micro-fractures leading to occurrences of pain. Furthermore, the localized distribution or “bolus” of material typically requires large volumes of material to be injected which can lead to increased patient exposure to implant material.
Accordingly, there is a need in the art for a vertebroplasty method that employs a material that does not suffer from the above drawbacks. The present invention fulfills this need by employing methods that utilize materials that can flow and interdigitate into the vertebral body, in small volumes.